CDIST-TYPE(7)

NAME
cdist-type - Functionality bundled

SYNOPSIS

__TYPE ID --parameter value [--parameter value ...]

__TYPE --parameter value [--parameter value ...] (for singletons)

DESCRIPTION

Types are the main component of cdist and define functionality. If you use cdist, you’ll write a type for every functionality you would like to use.

HOW TO USE A TYPE

You can use types from the initial manifest or the type manifest like a normal command:

    # Creates empty file /etc/cdist-configured
    __file /etc/cdist-configured --type file
    # Ensure tree is installed
    __package tree --state installed

A list of supported types can be found in the cdist-reference(7) manpage.

SINGLETON TYPES

If a type is flagged as a singleton, it may be used only once per host. This is useful for types which can be used only once on a system. Singleton types do not take an object name as argument.

Example:

    # __issue type manages /etc/issue
    __issue
    # Probably your own type - singletons may use parameters
    __myfancysingleton --colour green

HOW TO WRITE A NEW TYPE

A type consists of

    • parameter (optional)

    • manifest (optional)

    • singleton (optional)

    • explorer (optional)

    • gencode (optional)

Types are stored below cdist/conf/type/. Their name should always be prefixed with two underscores (__) to prevent collisions with other executables in $PATH.

To implement a new type, create the directory cdist/conf/type/__NAME.

DEFINING PARAMETERS

Every type consists of required, optional and boolean parameters, which must each be declared in a newline separated file in parameter/required, parameter/required_multiple, parameter/optional, parameter/optional_multiple and parameter/boolean. Parameters which are allowed multiple times should be listed in required_multiple or optional_multiple respectively. All other parameters follow the standard unix behaviour "the last given wins". If either is missing, the type will have no required, no optional, no boolean or no parameters at all.

Default values for optional parameters can be predefined in parameter/default/<name>.

Example:

    echo servername >> cdist/conf/type/__nginx_vhost/parameter/required
    echo logdirectory >> cdist/conf/type/__nginx_vhost/parameter/optional
    echo loglevel >> cdist/conf/type/__nginx_vhost/parameter/optional
    mkdir cdist/conf/type/__nginx_vhost/parameter/default
    echo warning > cdist/conf/type/__nginx_vhost/parameter/default/loglevel
    echo server_alias >> cdist/conf/type/__nginx_vhost/parameter/optional_multiple
    echo use_ssl >> cdist/conf/type/__nginx_vhost/parameter/boolean

USING PARAMETERS

The parameters given to a type can be accessed and used in all type scripts (e.g manifest, gencode-, explorer/). Note that boolean parameters are represented by file existence. File exists → True, file does not exist → False

Example: (e.g. in cdist/conf/type/__nginx_vhost/manifest)

    # required parameter
    servername="$(cat "$__object/parameter/servername")"
    # optional parameter
    if [ -f "$__object/parameter/logdirectory" ]; then
       logdirectory="$(cat "$__object/parameter/logdirectory")"
    fi
    # optional parameter with predefined default
    loglevel="$(cat "$__object/parameter/loglevel")"
    # boolean parameter
    if [ -f "$__object/parameter/use_ssl" ]; then
       # file exists -> True
       # do some fancy ssl stuff
    fi
    # parameter with multiple values
    if [ -f "$__object/parameter/server_alias" ]; then
       for alias in $(cat "$__object/parameter/server_alias"); do
          echo $alias > /some/where/usefull
       done
    fi

INPUT FROM STDIN

Every type can access what has been written on stdin when it has been called. The result is saved into the stdin file in the object directory.

Example use of a type: (e.g. in cdist/conf/type/__archlinux_hostname)

    __file /etc/rc.conf --source - << eof
    ...
    HOSTNAME="$__target_host"
    ...
    eof

If you have not seen this syntax (<< eof) before, it may help you to read about "here documents".

In the __file type, stdin is used as source for the file, if - is used for source:

        if [ -f "$__object/parameter/source" ]; then
            source="$(cat "$__object/parameter/source")"
            if [ "$source" = "-" ]; then
                source="$__object/stdin"
            fi
        ....

WRITING THE MANIFEST

In the manifest of a type you can use other types, so your type extends their functionality. A good example is the __package type, which in a shortened version looks like this:

    os="$(cat "$__global/explorer/os")"
    case "$os" in
          archlinux) type="pacman" ;;
          debian|ubuntu) type="apt" ;;
          gentoo) type="emerge" ;;
          *)
             echo "Don't know how to manage packages on: $os" >&2
             exit 1
          ;;
    esac
    __package_$type "$@"

As you can see, the type can reference different environment variables, which are documented in cdist-reference(7).

Always ensure the manifest is executable, otherwise cdist will not be able to execute it. For more information about manifests see cdist-manifest(7).

SINGLETON - ONE INSTANCE ONLY

If you want to ensure that a type can only be used once per target, you can mark it as a singleton: Just create the (empty) file "singleton" in your type directory:

    touch cdist/conf/type/__NAME/singleton

This will also change the way your type must be called:

    __YOURTYPE --parameter value

As you can see, the object ID is omitted, because it does not make any sense, if your type can be used only once.

THE TYPE EXPLORERS

If a type needs to explore specific details, it can provide type specific explorers, which will be executed on the target for every created object.

The explorers are stored under the "explorer" directory below the type. It could for instance contain code to check the md5sum of a file on the client, like this (shortened version from the type __file):

    if [ -f "$__object/parameter/destination" ]; then
       destination="$(cat "$__object/parameter/destination")"
    else
       destination="/$__object_id"
    fi
    if [ -e "$destination" ]; then
       md5sum < "$destination"
    fi

WRITING THE GENCODE SCRIPT

There are two gencode scripts: gencode-local and gencode-remote. The output of gencode-local is executed locally, whereas the output of gencode-remote is executed on the target. The gencode scripts can make use of the parameters, the global explorers and the type specific explorers.

If the gencode scripts encounters an error, it should print diagnostic messages to stderr and exit non-zero. If you need to debug the gencode script, you can write to stderr:

    # Debug output to stderr
    echo "My fancy debug line" >&2
    # Output to be saved by cdist for execution on the target
    echo "touch /etc/cdist-configured"

HINTS FOR TYPEWRITERS

It must be assumed that the target is pretty dumb and thus does not have high level tools like ruby installed. If a type requires specific tools to be present on the target, there must be another type that provides this tool and the first type should create an object of the specific type.

If your type wants to save temporary data, that may be used by other types later on (for instance file), you can save them in the subdirectory "files" below $object (but you must create it yourself). cdist will not touch this directory.

If your type contains static files, it’s also recommended to place them in a folder named "files" within the type (again, because cdist guarantees to never ever touch this folder).

HOW TO INCLUDE A TYPE INTO UPSTREAM CDIST

If you think your type may be useful for others, ensure it works with the current master branch of cdist and have a look at cdist-hacker(7) on how to submit it.

SEE ALSO

    • cdist-explorer(7)

    • cdist-hacker(7)

    • cdist-stages(7)

    • cdist-tutorial(7)

COPYING

Copyright (C) 2011-2012 Nico Schottelius. Free use of this software is granted under the terms of the GNU General Public License version 3 (GPLv3).

AUTHOR

Nico Schottelius <nico-cdist--@--schottelius.org>
    Author.